This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-272260, filed Sep. 7, 2001; and No. 2001-272261, filed Sep. 7, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an exhaust emission control device for purifying exhaust gas from a diesel engine.
2. Description of the Related Art A DPF (diesel particulate filter) of a continuous-regeneration type that uses an oxidizing catalyst and a particulate filter is known as a device for purifying exhaust gas of a diesel engine. In the purifying device of this type, NO in the exhaust gas is oxidized and changed into NO2 with the oxidizing catalyst, so that soot (consisting mainly of carbon) in the particulate filter can be burned with NO2 in a relatively low temperature range.
If excessive soot is deposited on the particulate filter of the continuous-regeneration DPF, the engine output lowers, and besides, the filter may possibly be melted down due to an extraordinarily high temperature as the soot is burned. Accordingly, the particulate filter must be heated up with use of some heat-up means to burn the deposited soot compulsively (for compulsive regeneration) in a timely manner. As is generally known, the compulsive regeneration is achieved by injecting a fuel (for so-called post-injection) in the expansion stroke of the engine.
Described in Jpn. Pat. Appln. KOKAI Publication No. 7-259533, moreover, is a technique such that an oxidizing catalyst carried on a particulate filter is heated up by increasing the injection quantity during the expansion or exhaust stroke of an engine when the catalyst is inactive (or cold).
This technique of using surplus fuel to heat up the oxidizing catalyst, however, has the problem of a low fuel-efficiency. When the engine is cold or in a low-load operation with the oxidizing catalyst at low temperature, moreover, the catalyst cannot cause the injected fuel easily to react, so that a satisfactory heat-up effect cannot be obtained.
The object of the present invention is to provide an exhaust emission control device, capable of effectively heating up an oxidizing catalyst and restraining the fuel-efficiency from lowering.
In order to achieve the above object, an exhaust emission control device of an engine according to the present invention is configured to regenerate a particulate filter in a manner such that the injection timing for main injection of the fuel injection of the engine is delayed and/or the exhaust gas reflux quantity is increased if the temperature of an oxidizing catalyst in an engine passage on the upper-stream side of the particulate filter is not higher than a given value, and that a component to be oxidized by the catalyst is then supplied to the catalyst.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.